Esterification reactions on syndiotactic poly(methallyl alcohol)—III. Esterification with cyclic carboxylic acid anhydrides

The esterification of syndiotactic poly(2-methallyl alcohol) by aromatic and aliphatic cyclic acid anhydrides, including N^α-protected (spl)-aminodicarboxylic acid anhydrides is reported. Conditions are chosen such that defined partial or complete conversions are obtained. The structures of the products, including the degree of conversion, are determined by ¹H-and ¹³C-NMR. By potentiometric titration, the solubility in water of some of the polymers and their dissociative and conformational behaviour are studied.     

Esterification reactions on syndiotactic poly(2-methallyl alcohol). II. Esterification with protected (L)-aspartic and (L)-glutamic acids

The esterification of syndiotactic poly(2-methallyl alcohol) by N^α- and O^ω- protected aspartic and glutamic acids by the DCC/HOBT method is described. Depending on the extent of conversion, either homopolymers or copolymers are obtained. Both homo- and copolymers are characterized by ¹H- and ¹³C-NMR. A second route to the homopolymers has been followed, whereby the poly(2-methallyl alcohol) is first esterified by N^α-protected aspartic or glutamic acid anhydrides and, in a second step, the resulting free carboxyl group on the side chain is esterified by alcohols which are the same as the alcohol moiety of the O^ω-protecting groups. Because the homopolymers were identical to those of the first route, the formation of α-esters with the acid anhydrides is indicated.     

Reaction of syndiotactic poly(methacrylic acid hydrazide) with functional carboxylic acids

As a highly reactive tactic vinyl polymer, syndiotactic poly(methacrylic acid hydrazide) (s-PMH) was prepared from syndiotactic poly(methyl methacrylate) (s-PMMA) by hydrazinolysis. The s-PMH served as the starting polymer to prepare other tactic vinyl homopolymers having optically active functional carboxylic acids or N-protected amino acids as side chains. The condensation of the acids was carried out in water by water-soluble carbodiimides. Conversion was followed by pH and the resulting homopolymers characterized by ¹H- and ^13C-NMR spectroscopy. The NMR-spectra were assigned by comparison with low molecular weight model compounds, derived from pivalic acid hydrazide. In a third on-polymer reaction, the OH-groups present in the side chains of some of the polymers were employed for adding an optically active isocyanate to yield branched side chains.     

Synthesis of polyacrylamide samples of known steric structure

The esterification of atactic, syndiotactic and isotactic samples of poly(acrylic acid) by phenol and p-nitrophenol, carried out at 95° in the presence of POCl₃, led only to atactic poly(phenyl and p-nitrophenyl acrylates) respectively, as shown by ¹H-NMR (250 MHz). These polymers and isotactic poly(phenyl acrylate), prepared by anionic polymerization of phenyl acrylate with n-butyllithium, when reacted with ammonia led to bridged polyacrylimides or to linear atactic or isotactic polyacrylamides according to the reaction conditions. Anionic homopolymerization of p-nitrophenyl acrylate did not occur.     

Interaction of polyanions with electroneutral liposomes in a slightly acidic medium

In this study, the interaction between poly(styrene sulfonic acid), polyacrylic acid, poly(meth-acrylic acid), poly(L-glutamic acid), poly(vinyl sulfate), and ternary copolymer of styrene with maleic anhydride and methacrylic acid (3: 2: 1), as well as DNA with lipid vesicles composed of zwitterion (electroneutral) lipid phosphatidylcholine, has been investigated. The methods of centrifuge ultrafiltration and dynamic light scattering reveal that, at pH 4.2, all polyacids under study are effectively adsorbed on the phospholipid membrane. The polymer-membrane complex is stabilized by hydrogen bonds and hydrophobic interactions in addition to electrostatic bonds. Even though, to a greater or lesser extent, all polyacids are capable of undergoing adsorption on the membrane in a slightly acidic medium, their effect on the membrane permeability is substantially different and is correlated with the ability of a polymer to form multiple interactions with phospholipid molecules. Poly(acrylic acid), poly(methacrylic acid), poly(styrene sulfonic acid), and the ternary copolymer of styrene with maleic anhydride and methacrylic acid can produce the membrane pores that are permeable to low-molecular-mass compounds. At the same time, poly(L-glutamic acid), poly(vinyl sulfate), and DNA exert no effect on the membrane permeability, although they are sorbed on the membrane surface.     

Preparation and (13C)NMR spectroscopy of stereoregular poly(methacrylic acid)

Several procedures for synthesis of stereoregular poly(methacrylic acid) have been examined and the polymer characterized by (¹³C)NMR. Using d⁶ DMSO as solvent for spectroscopy gives better spectra than those previously obtained using aqueous solutions and stereochemical splittings can be resolved in the methyl signals. Free-radical polymerization in toluene solution is a Bernouilli process giving mainly heterotactic/syndiotactic polymer. Polymers produced with free-radical initiation in aqueous solution have a higher, and pH dependent, content of syndiotactic triads. A previously described procedure for producing regular polymers by hydrolysis of poly(trimethylsilyl methacrylate) requires modification to produce isotactic contents of above 90% and does not give truly syndiotactic polymer. In contrast, polymerization with γ-radiation can produce polymers with close to 90% of syndiotactic triads.     

Electroactive films of interpolymer complexes of polyaniline with polyamidosulfonic acids: advantageous features in some possible applications

With the purpose of determining prospects of possible applications of interpolymer complexes of polyaniline (PANI) with poly(amidosulfonic acid)s, we have performed a comparative study of polyaniline films prepared by electrochemical polymerization of aniline in the presence of the polyacids distinguished by different rigidities of the polymer backbone: (1) poly(2-acrylamido-2-methyl-1-propanosulfonic acid) (flexible backbone); (2) poly-p,p′-(2,2′-disulfoacid)-diphenylen-iso-phthalamid (semi-rigid backbone); (3) poly-p,p′-(2,2′-disulfoacid)-diphelylen-tere-phthalamid (rigid backbone); and (4) a copolymer of the latter two acids with monomer feed ratio 1:1 (co-PASA). Spectroelectrochemical studies in the UV–vis–NIR range showed that PANI complexes with rigid-chain polyacids far more effectively modulate absorbance in the Vis–NIR range and can be considered as promising candidates for “smart windows” development. Due to the presence of bulky unmovable polyacid anion, PANI interpolymer complexes (particularly those with the semi-rigid-chain polyacids) possess much wider pH range of electroactivity than common PANI, which is of great importance for biosensor applications. The interpolymer complexes with flexible-chain and semi-rigid-chain polyacids exhibit good optical response to ammonia vapors at conditions of high humidity, which make them promising materials for the development of ammonia optical sensors.     

Synthesis of a novel syndiotactic poly(macromonomer) consisting of styrene‐terminated polyisoprene macromonomers using half‐titanocene catalysts

Homopolymerization of a styrene‐terminated polyisoprene macromonomer (SIPM) by half‐titanocene catalysts in combination with methylaluminoxane (MAO) was investigated. Polymerization of the SIPM with CpTiCl₃‐MAO as the catalyst was found to proceed readily to give a high molecular weight polymer. ¹H and ¹³C NMR spectra of the poly(SIPM) after ozonolysis of the isoprene side chain revealed that poly(SIPM) is a highly syndiotactic polymer. Syndiotactic poly(SIPM) is soluble in usual solvents in spite of having highly syndiotactic sequences on its main chain and a considerable degree of polymerization.     

1H-NMR of the esterification of syndiotactic poly(methacrylic acid) with carbodiimides—II. Esterification with benzylalcohol and trifluoroethanol

The partial esterification of syndiotactic poly(methacrylic acid) with benzyl alcohol or trifluoroethanol and dicyclohexylcarbodiimide as a condensing agent has been studied, evaluating triad and pentad probabilities by ¹H-NMR. The mechanism of this esterification leads to a tendency toward alternation for esterified and unesterified monomer units along the chain and to a limiting conversion. Only a moderate approximation of triad and pentad probabilities by conditional probabilities of first and second order was possible. The esterification of poly(methacrylic acid) with trifluoroethanol has been carried out also in conc H₂SO₄ and leads to a random distribution of monomer units.     

Synthesis of polar block grafted syndiotactic polystyrenes via a combination of iridium‐catalyzed activation of aromatic C?H bonds and atom transfer radical polymerization

A combination of iridium‐catalyzed C H activation/borylation and atom transfer radical polymerization (ATRP) was used to generate polar graft copolymers of syndiotactic polystyrene (sPS). The borylation at aromatic C H bonds of sPS and subsequent oxidation of boronate ester proceeded without negatively affecting the molecular weight properties and the tacticity of sPS. A macroinitiator suitable for ATRP could be synthesized by the esterification of 2‐bromo‐2‐methylpropionyl bromide and hydroxy‐functionalized sPS. The graft polymerizations of methyl methacrylate and tert‐butyl acrylate from the macroinitiator using ATRP afforded polar block grafted sPS materials, syndiotactic polystyrene‐graft‐poly(methyl methacrylate) (sPS‐g‐PMMA) and syndiotactic polystyrene‐graft‐poly(tert‐butyl acrylate) (sPS‐g‐PtBA). The latter was hydrolyzed to yield an amphiphilic graft copolymer, syndiotactic polystyrene‐graft‐poly(acrylic acid) (sPS‐g‐PAA). The structures of the copolymers were characterized by NMR and FTIR spectroscopies. Size exclusion chromatography and ¹H NMR spectroscopy were used to study any changes in the molecular weight properties from the parent polymer. A decrease in the hydrophobicity of the graft copolymers was confirmed by water contact angle measurements. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6655–6667, 2009     

Stereoregularity of poly(2-vinylpyridine) determined by 1H-NMR and 13C-NMR spectroscopy

In order to determine the stereoregularity of poly(2-vinylpyridine), 2-vinylpyridine-β,β-d₂ was synthesized. The ¹H-NMR spectra of the deuterated polymer in D₂SO₄ and o-dichlorobenzene solutions showed three peaks, which were assigned to triad tacticities. Since the absorptions of heterotactic and syndiotactic triads of methine protons overlap those of methylene protons in nondeuterated polymers, only isotactic triad intensities can be obtained from the ¹H-NMR spectra of nondeuterated poly(2-vinylpyridine). The ¹³C-NMR spectra of poly(2-vinylpyridine) were obtained in methanol and sulfuric acid solutions. In methanol solution the absorption was split into three groups, which cannot be explained by triads, and in sulfuric acid solution several peaks were observed. These splittings may be due to pentad tacticity. The results show that poly(2-vinylpyridine) obtained by radical polymerization is an atactic polymer.     

Nickel catalyzed decarboxylative alkylation of aryl triflates with anhydrides

Aliphatic acid anhydrides are the versatile building blocks and the new method for the conversion of anhydrides is thus of great significance. Herein, we report the decarboxylative alkylation of aryl triflates with aliphatic acid anhydrides via nickel catalysis. This novel method provides a facile access to construct Csp²-Csp³ bond. In addition, this method is compatible with a broad array of functional groups and exhibits good substrates scope.     

A study of radical polymerization of N-vinylpyrrolidone in the presence of poly(methacrylic acid) templates by DSC

The template polymerization of N-vinylpyrrolidone (NVP) along syndiotactic poly(methacrylic acid) (s1-PMAA) templates has been studied by differential scanning calorimetry (DSC) using the scanning as well as the isothermal technique. The resulting Arrhenius plot covers a temperature range between 65 and 120°C and two parts can be distinguished. Below 80°C the overall activation energy, E_a, and entropy ΔS^≠, are 76 kJ · mol^?1 and ?79 J · mol^?1 · K^?1 respectively, in excellent agreement with previous dilatometric results. These values differ slightly from those of the blank polymerization leading to rate enhancement by a factor of only two. The small difference in activation parameters is explained by the occurrence of desolvation of st-PMAA chains during propagation of the polyvinylpyrrolidone (PVP) radicals along the template. Above 80°C, the decreasing tendency to form complexes between PVP and st-PMAA results in a decreasing template effect and a gradual change of apparent E_a and ΔS^≠ values towards those of the blank polymerization. Similar results were obtained with atactic and isotactic PMAA templates, but smaller rate enhancements were observed due to weaker complex formation.     

1H-NMR of the esterification of syndiotactic poly(methacrylic acid) with carbodiimides—I. Esterification with methanol

The esterification of syndiotactic poly(methacrylic acid) with methanol in the presence of dicyclohexylcarbodiimide as a condensing agent has been studied, evaluating triads by ¹H-NMR. The reaction proceeds via a cyclic anhydride as an intermediate, which with methanol then forms the ester. This mechanism leads to a limiting conversion and to a tendency toward alternation for the sequencing of esterified and unesterified monomer units along the chain. The statistics of the methyl methacrylate-methacrylic acid copolymers can be approximated by conditional probabilities of first order.     

Synthesis and in vitro degradation of poly(alkylene carbonate anhydride)

A novel degradable poly(alkylene carbonate anhydride) (PACA) was synthesized by the melt polycondensation reaction of the corresponding mixed anhydrides of the dicarboxylic acid derived from oligo(tetramethylene carbonate)diol (OTMCD) and oligo(hexamethylene carbonate)diol (OHMCD). The polymer's structure was confirmed by IR and ¹H NMR spectroscopy. DSC analysis showed PACA had a low T_g (< –30°C). In vitro degradation tests indicated that the degradation rate of poly(alkylene carbonate) was more controlled with the incorporation of anhydride groups.     

Molecular modeling of polymers. 10. Characterization of conformational transitions of poly(acrylic acid) and poly(methacrylic acid) using dyad structures

The conformational profiles of nearest side-chain neighbors, methylene-dyad structures, of poly(acrylic acid), PAA, and poly(methacrylic acid), PMA, were determined as a function of tacticity, extent of ionization, and presence of counterion. The dominant backbone conformer states are quite similar for both isotactic and syndiotactic diads in a common charge state. Thus, the overall dimensional properties of isotactic syndiotactic and atactic chains of PAA or PMA, based upon dyad interactions, are predicted to be alike for a given charge state. Significant deviations from precise t, g⁺, and g^? states are found for the dyad minimum energy conformations. The rod-to-coil and coil-to-rod transitions observed in PAA and PMA, respectively, as a function of increasing counterion concentration can be explained, to a large extent, by the conformational profiles of the corresponding dyad model structures. © 1994 John Wiley & Sons, Inc.     

Synthesis of syndiotactic-polystyrene-graft-poly(methyl methacrylate) and syndiotactic-polystyrene-graft-atactic-polystyrene by atom transfer radical polymerization

Syndiotactic polystyrene graft copolymers, including syndiotactic-polystyrene-graft-poly(methyl methacrylate) and syndiotactic-polystyrene-graft-atactic-polystyrene, were synthesized by atom transfer radical polymerization (ATRP) using bromoacetylated syndiotactic polystyrene as macroinitiator and copper bromide combined with 2,2′-bipyridine as catalyst. The macroinitiator was prepared from the acid-catalyzed halogenation reaction of partially acetylated syndiotactic polystyrene, which was synthesized in a heterogeneous process with acetyl chloride and anhydrous aluminum chloride in carbon disulfide. The graft copolymers were characterized by ¹H- and ¹³C-NMR spectra.     

Stereoregularity of Poly(methyl Methacrylate) Obtained by New Complex Bases

The stereoregularity of poly(methyl methacrylate) obtained with complex bases in various solvents was determined by ¹H-NMR spectroscopy. Polymethyl methacrylates produced by complex bases are mostly hetero and/or syndiotactic and obey Bernoullian statistics.     

Highly efficient heterogeneous acylations of aromatic compounds with acid anhydrides and carboxylic acids by montmorillonite-enwrapped titanium as a solid acid catalyst

Montmorillonite-enwrapped titanium hydroxide species (Ti⁴⁺-mont) acted as a highly efficient heterogeneous acid catalyst for the acylation of aromatic compounds with acid anhydrides or carboxylic acids. The catalytic activity of the Ti⁴⁺-mont was higher than those of other acid catalysts such as zeolites, SO ₄ ^2? /ZrO₂ and p-toluenesulfonic acid. For example, the reaction of anisole with dodecanoic acid in the presence of the Ti⁴⁺-mont catalyst gave 1-(4-methoxyphenyl)-1-dodecanone in 97% yield. Furthermore, the Ti⁴⁺-mont catalyst was easily separated from the reaction mixture and was recyclable.